JP6189426B2 - Magnetoresistive gear sensor - Google Patents

Description

  The present invention relates to the technical field of gear sensors, and more particularly to a magnetoresistive gear sensor using an MTJ element as a sensing element.

  The gear sensor is mainly applied to an automatic control system, and measures a rotation speed and a rotation direction of a gear. Currently, commonly used gear sensors are optical sensors and magnetic sensors. In the mechanical rotation system, the magnetic sensor has a great advantage over the optical sensor against bad environments such as vibration, shock, and oil contamination. In the known technology, there are many different types of magnetic sensors, for example, a magnetic sensor using a Hall element, an anisotropic magnetoresistance (AMR) element, or a giant magnetoresistance (GMR) as a sensing element. .

  Magnetic sensors using Hall elements as sensing elements have very low sensitivity, and normally it is necessary to increase the sensitivity of the Hall elements by expanding the magnetic field using a flux concentrator. The size and weight of the magnetic sensor increases. In addition, a magnetic sensor using a Hall element as a detection element has disadvantages such as high power consumption and poor linearity. The sensitivity of the AMR element is higher than that of the Hall element, but the linear operation range of the AMR element is narrow. A magnetic sensor using an AMR element as a detection element needs to be set / reset by arranging a “set / reset” coil, which complicates the manufacturing process of the magnetic sensor using the AMR element as a detection element. In addition, the size and power consumption of a magnetic sensor using an AMR element as a sensing element increase. A magnetic sensor using a GMR element as a detection element has higher sensitivity than a sensor using a Hall element as a detection element, but the linear operation range of the magnetic sensor using a GMR element as a detection element is narrow. Further, since the response curve of the GMR element is even-symmetrical, a magnetic sensor using the GMR element as a sensing element can measure only a unipolar gradient magnetic field and cannot measure a bipolar gradient magnetic field.

In recent years, a new type of magnetoresistive effect sensor, that is, a magnetic sensor using a magnetic tunnel junction (MTJ) element as a detection element has begun to be applied industrially. The principle of operation of a magnetic sensor using an MTJ element as a detection element is to detect a magnetic field by using a tunnel magnetoresistance (TMR) effect of a magnetic multilayer film material. The MTJ element has a higher resistance change rate than the previously used AMR element and GMR element. Compared to the Hall element, the MTJ element has good temperature stability, high sensitivity, low power consumption, and good linearity, and does not require an extra flux concentrator. Compared to AMR elements, MTJ elements have good temperature stability, high sensitivity, a wide linear operating range, and do not require an extra “set / reset” coil structure. Compared to GMR elements, MTJ elements have good temperature stability, high sensitivity, low power consumption, and a wide linear operating range.

Normally, the magnetic sensor for gear detection has a structure employing a printed circuit board (PCB) type. A PCB-type gear sensor is usually composed of a magnetic sensor chip, a peripheral electric circuit, and a permanent magnet. The magnetic sensor chip detects a change in the external magnetic field H _apply generated by the permanent magnet at the physical position where the magnetic sensor chip is located, and outputs a detection signal. The peripheral electric circuit outputs a detection signal output from the magnetic sensor chip. Processing and conversion are performed. The change in the external magnetic field H _apply caused by the permanent magnet at the physical location where the magnetic sensor chip is located is very weak. Therefore, in the application of the PCB type gear sensor, it is an urgent task to prevent interference caused by an interference magnetic field other than the external magnetic field H _apply generated by the permanent magnet.

Although the MTJ element has high sensitivity, a magnetic sensor using the MTJ element as a sensing element has the following drawbacks.

(1) The amount of the external magnetic field _Happly generated by the permanent magnet is large along the detection direction of the MTJ element, causing the MTJ element to deteriorate in performance by deviating from the linear operation range, and further operating when the MTJ element reaches saturation. It invites you to become impossible.

(2) When the magnetic sensor chip detects a change in the external magnetic field H _apply generated by the permanent magnet at the physical position where the magnetic sensor chip is located, the magnetic sensor chip is susceptible to interference by an interference magnetic field other than the external magnetic field H _apply generated by the permanent magnet.

(3) The position of the gear teeth cannot be determined, and when the gear teeth are missing, the specific position of the missing teeth cannot be determined.

(4) The direction of gear movement cannot be determined.

(5) It is difficult to realize large-scale production at low cost.

Therefore, a gear sensor that can accurately detect the movement state of the gear is desired.

An object of the present invention is to provide a magnetoresistive gear sensor.
The magnetoresistive gear sensor provided in the present invention includes a magnetic sensor chip and a first permanent magnet, and the magnetic sensor chip includes at least one bridge, and each arm of the bridge includes at least one MTJ element group.

  The magnetoresistive gear sensor further includes a concave soft magnetic body disposed between the magnetic sensor chip and the first permanent magnet, and the opening of the soft magnetic body faces the magnetic sensor chip. It is preferable that

  Preferably, the at least one MTJ element group is a plurality of MTJ element groups, and the plurality of MTJ element groups are connected in series and / or in parallel.

  The plurality of MTJ element groups are preferably connected in series and / or in parallel in the same detection direction.

  All the arms including the MTJ element group preferably have the same detection direction.

  The bridge is preferably a half bridge, a full bridge, or a double full bridge.

  Each MTJ element group preferably includes a plurality of MTJ elements connected in series and / or in parallel.

  Each MTJ element group preferably includes a plurality of MTJ elements connected in series and / or in parallel in the same detection direction.

  Each MTJ element has a multilayer structure, and preferably includes a pinning layer, a pinned layer, a tunnel barrier layer, and a magnetic free layer which are sequentially deposited.

  A pair of second permanent magnets are provided on both sides of each MTJ element group, and each pair of second permanent magnets has a detection direction of the corresponding MTJ element group in order to provide a bias magnetic field to the MTJ element group. It is preferable that the arrangement is inclined.

  A pair of second permanent magnets are provided on both sides of each MTJ element group, and each pair of second permanent magnets has a detection direction of the corresponding MTJ element group in order to cancel the nail coupling magnetic field of the MTJ element group. It is preferable that they are arranged inclined.

  In order to further cancel the nail coupling magnetic field of the MTJ element group, it is preferable that the second permanent magnets of each pair are arranged to be inclined with respect to the detection direction of the corresponding MTJ element group.

  Each MTJ element has a multilayer structure, and preferably includes a pinning layer, a pinned layer, a tunnel barrier layer, a magnetic free layer, and a bias layer, which are sequentially deposited.

  Each MTJ element preferably further includes an isolation layer provided between the magnetic free layer and the bias layer.

  It is preferable that the magnetoresistive gear sensor further includes a control circuit electrically connected to the magnetic sensor chip.

  It is preferable that the control circuit determines a tooth position based on a correspondence relationship between a voltage signal output from the magnetic sensor chip and a gear tooth position.

  The magnetic sensor chip includes a double full bridge, each arm of the double full bridge includes an MTJ element group, and the control circuit determines a movement direction of a gear based on a voltage signal output from the magnetic sensor chip. Is preferred.

  It is preferable that the magnetoresistive gear sensor further includes a casing.

The present invention has the following beneficial effects.

(1) The sensor uses an MTJ element as a detection element, and has a higher temperature stability, higher sensitivity, and lower power consumption than the sensor using a Hall element, an AMR element, or a GMR element as a detection element. Good linearity, wide linear operating range, and simple structure.

(2) The sensor is provided with a concave soft magnetic material, and the amount of the MTJ element in the magnetic sensor chip is linearly reduced by reducing the amount along the detection direction of the MTJ element in the external magnetic field generated by the permanent magnet. It can be ensured that it operates within the operating range, and the performance of the sensor can be greatly improved.

(3) By adopting a full bridge for the magnetic sensor chip of the sensor, the sensor is less susceptible to interference by an interference magnetic field other than an external magnetic field generated by a permanent magnet.

(4) In one preferred embodiment, a pair of inclined permanent magnets are arranged on both sides of the MTJ element group, and the amount perpendicular to the detection direction of the MTJ element in the magnetic field generated by the inclined permanent magnet is equal to the MTJ element. To provide a bias magnetic field. The saturation magnetic field of the MTJ element can be adjusted by changing the bias magnetic field, whereby a highly sensitive sensor can be obtained, or a sensor with a different sensitivity can be realized as required.

(5) In one preferred embodiment, a pair of tilted permanent magnets are arranged on both sides of the MTJ element group, and the amount along the MTJ element detection direction in the magnetic field generated by the tilted permanent magnet is the MTJ element group. Can be canceled, thereby ensuring that the operating point of the MTJ element is located in its linear operating range and improving the linearity of the sensor.

(6) In another preferred embodiment, a bias layer is disposed on the magnetic free layer of the MTJ element, and the bias layer can provide a bias magnetic field perpendicular to the detection direction of the MTJ element to the magnetic free layer. . The saturation magnetic field of the MTJ element can be adjusted by changing the bias magnetic field, whereby a highly sensitive sensor can be obtained, or a sensor with a different sensitivity can be realized as required.

(7) The sensor can determine the position of the tooth of the gear, and can determine the position of the missing tooth even when the tooth of the gear is missing.

(8) The sensor can determine not only the speed of movement of the gear but also the direction of movement of the gear.

(9) The sensor is applied not only to a linear gear but also to a circular gear.

(10) The sensor is advantageous for realizing large-scale production at low cost.

FIG. 1 is a schematic diagram of the structure of the first MTJ element 11 provided in Example 1 of the present invention. FIG. 2 is a response curve diagram of the resistance of the first MTJ element 11 with respect to the external magnetic field H _apply in the ideal state, and the external magnetic field H _apply is along the detection direction of the first MTJ element 11. FIG. 3 is a response curve diagram of the resistance of the first MTJ element 11 with respect to the external magnetic field H _apply during actual use, and the external magnetic field H _apply is along the detection direction of the first MTJ element 11. FIG. 4 is a schematic diagram in which a plurality of first MTJ elements are connected in series to form one first MTJ element group 13. FIG. 5 is a schematic diagram in which a pair of inclined permanent magnets 14 are arranged on both sides of the first MTJ element group 13. FIG. 6 is a cross-sectional view of the magnetic field distribution around a pair of inclined permanent magnets arranged on both sides of the first MTJ element group 13. FIG. 7 is a plan view in which a pair of inclined permanent magnets 14 are arranged on both sides of the first MTJ element group 13. FIG. 8 is a plan view of the physical position of the half bridge 15. FIG. 9 is an equivalent circuit diagram of the half bridge 15 shown in FIG. FIG. 10 is a plan view of the physical position of the full bridge 16. FIG. 11 is an equivalent circuit diagram of the full bridge 16 shown in FIG. FIG. 12 is a curve diagram of the actual output voltage of the magnetic field sensor employing the full bridge 16. FIG. 13 is a plan view of the physical position of the double full bridge 17. FIG. 14 is an equivalent circuit diagram of the double full bridge 17 shown in FIG. FIG. 15 is a schematic diagram of the structure of the magnetoresistive gear sensor 18 provided in the first embodiment of the present invention. FIG. 16 is a schematic diagram of a sinusoidal voltage signal output from the magnetoresistive gear sensor 18 provided in the first embodiment of the present invention. FIG. 17 is a schematic diagram of sine wave and rectangular wave voltage signals output from the magnetoresistive gear sensor 18 provided in the first embodiment of the present invention when gear teeth are missing. FIG. 18 is a schematic diagram of two voltage signals output from the magnetoresistive gear sensor 18 provided in the first embodiment of the present invention. FIG. 19 is a schematic diagram of the structure of the second MTJ element 21 provided in Embodiment 2 of the present invention.

  Hereinafter, the contents of the present invention will be described in detail with reference to the drawings and embodiments.

<Example 1>
FIG. 1 is a schematic diagram of the structure of the first MTJ element 11 provided in Example 1 of the present invention. The first MTJ element 11 has a multilayer film structure. As shown in FIG. 1, the insulating layer 112, the bottom electrode layer 113, the pinning layer 114, the pinned layer 115, and the tunnel barrier layer 116 sequentially deposited on the substrate 111. The magnetic free layer 117 and the top electrode layer 118 are included. The pinned layer 115 and the magnetic free layer 117 are ferromagnetic layers, and materials thereof include, for example, Fe, Co, Ni, FeCo, FeNi, FeCoB, or FeCoNi. The pinned layer 115 is a composite layer formed of a ferromagnetic layer, a Ru layer, and a ferromagnetic layer. For example, the pinned layer 115 is a composite layer formed of a FeCo layer, a Ru layer, and a FeCo layer. By the exchange coupling between the pinning layer 114 and the pinned layer 115, the magnetic moment direction 1151 of the pinned layer 115 is fixed in one direction, and the magnetic moment direction 1151 is not changed by the action of the external magnetic field _Happly . The pinning layer 114 is an antiferromagnetic layer, and the material thereof includes, for example, PtMn, IrMn, or FeMn. The material of the tunnel barrier layer 116 includes, for example, MgO or Al ₂ O ₃ . The direction 1171 of the magnetic moment of the magnetic free layer 117 can be changed with the change of the external magnetic field _Happly . Due to the action of the external magnetic field H _apply , the magnetic moment direction 1171 of the magnetic free layer 117 gradually changes from a direction parallel to the magnetic moment direction 1151 of the pinned layer 115 to a direction antiparallel to the magnetic moment direction 1151 of the pinned layer 115. It is possible to change and vice versa. In this embodiment, the direction 1171 of the magnetic moment of the magnetic free layer 117 is defined as the detection direction of the first MTJ element 11. For the top electrode layer 118 and the bottom electrode layer 113, a nonmagnetic conductive material is usually used. As the material of the substrate 111, silicon, quartz, heat-resistant glass, GaAs or AlTiC is usually used. The area of the insulating layer 112 is larger than the area of the bottom electrode layer 113. The top electrode layer 118 and the bottom electrode layer 113 are used for electrical connection with other elements. In the present embodiment, the top electrode layer 118 and the bottom electrode layer 113 are electrically connected to the ohmmeter 12, for example, and the resistance of the first MTJ element 11 is measured.

The magnitude of the resistance of the first MTJ element 11 is related to the relative orientation of the magnetic moment between the magnetic free layer 117 and the pinned layer 115. When the magnetic moment direction 1171 of the magnetic free layer 117 is parallel to the magnetic moment direction 1151 of the pinned layer 115, the resistance of the first MTJ element 11 is the smallest, and the first MTJ element 11 is in a low resistance state. When the magnetic moment direction 1171 of the magnetic free layer 117 is antiparallel to the magnetic moment direction 1151 of the pinned layer 115, the resistance of the first MTJ element 11 is the largest, and the first MTJ element 11 is referred to as being in a high resistance state. By using a known technique, the resistance value of the first MTJ element 11 can be linearly changed between the high resistance state and the low resistance state in accordance with the change of the external magnetic field H _apply .

In an ideal state, a response curve diagram of the resistance of the first MTJ element 11 with respect to the external magnetic field H _apply is as shown in FIG. 2, and the external magnetic field H _apply is along the detection direction of the first MTJ element 11. When the first MTJ element 11 is in a low resistance state or a high resistance state, the response curve is saturated. For example, the resistance value of the first MTJ element 11 in the low resistance state is R _L , and the resistance value of the first MTJ element 11 in the high resistance state is R _H , for example. Between the high resistance state and the low resistance state, the resistance value R of the first MTJ element 11 changes to a linear shape with a change in the external magnetic field H _apply . The slope of the response curve of the resistance value R of the first MTJ element 11 with respect to the external magnetic field H _apply , that is, the rate of change of the resistance value R of the first MTJ element 11 with the external magnetic field H _apply is defined as the sensitivity of the first MTJ element 11. As shown in FIG. 2, in the response curve of the resistance of the first MTJ element 11 with respect to the external magnetic field H _apply, a straight line of H _apply = 0 is not axially symmetric, and a straight line of H _apply = H 2 _O is axially symmetric. Usually, H 2 _O is referred to as a Neel Coupling magnetic field. In the normal state, the range of the nail coupling magnetic field H 2 _O is 1-40 Oe.

As shown in FIG. 2, within the linear range of the response curve, the resistance value R of the first MTJ element 11 can be approximately expressed by the following equation.

In the formula (1), H _S represents a saturation magnetic field. The definition of the saturation magnetic field H _S is that when the Neel coupling magnetic field H _O = 0, the tangent of the linear range of the response curve of the resistance of the first MTJ element 11 to the external magnetic field H _apply and the tangent of the positive or negative saturation curve The value of the external magnetic field corresponding to the intersection. In an ideal state, the change in the resistance value R of the first MTJ element 11 due to the external magnetic field H _apply is a perfect linear relationship and has no hysteresis. In an actual situation, since the first MTJ element 11 has hysteresis, the response curve of the resistance of the first MTJ element 11 with respect to the external magnetic field H _apply is a single curve as shown in FIG. The actual sensor applications, due to defects constraints and material design of the magnetic sensor, the response curve of the resistance of the 1MTJ element 11 is further bent with respect to the external magnetic field H _{the apply.}

  In application, a plurality of first MTJ elements 11 can be connected in series and / or in parallel to form one first MTJ element group. In the present embodiment, the first MTJ element group 13 is formed by connecting six first MTJ elements 11 in series, and as shown in FIG. 4, the six first MTJ element groups 11 related to the first MTJ element group 13. The detection direction 1171 is the same. The first MTJ element group 13 is electrically connected to another element, for example, an ohmmeter 12. When the current 131 flows through the first MTJ element group 13, the direction of the current 131 is as shown in FIG. Under normal circumstances, the direction of the current 131 does not affect the resistance value of the MTJ element group 13. The resistance value of the first MTJ element group 13 can be adjusted by changing the number of the first MTJ elements 11 related to the first MTJ element group 13. One first MTJ element group 13 can be used as one arm of the bridge, and a plurality of first MTJ element groups 13 connected in series and / or in parallel can be used as one arm of the bridge.

A pair of inclined permanent magnets on both sides of the first MTJ element 11 or the first MTJ element group 13 to provide the bias magnetic field H _cross to the first MTJ element 11 or the first MTJ element group 13 and cancel the nail coupling magnetic field H 2 _O. 14 can be arranged. In the present embodiment, as shown in FIG. 5, for example, a pair of permanent magnets 14 is disposed on both sides of the first MTJ element group 13, and the permanent magnets 14 are inclined with respect to the detection direction of the first MTJ element group 13. Has been. After the permanent magnet 14 is magnetized, the magnetic field distribution around the first MTJ element group 13 is as shown in FIG. In the present embodiment, the shape of the permanent magnet 14 is, for example, a rectangular parallelepiped. As shown in FIG. 7, the residual angle of the angle between the long side of the permanent magnet 14 and the detection direction 1171 of the first MTJ element group 13 is defined as the inclination angle θ _sns of the permanent magnet 14. The length, width and thickness of each permanent magnet 14 are L, W and t, respectively, and the gap between the two permanent magnets 14 is G.

It is considered that the magnetic field H _{mag at} the gap position between the two permanent magnets 14 is generated by the magnetic charges at the edges of the two permanent magnets 14, and the magnetic field H _mag is related to the shape and boundary conditions of the permanent magnets 14. ing. As shown in FIG. 7, it is defined as the inclination angle theta _mag remanence _M r 141 angle with permanent magnets 14 between the remanence _M r 141 of the permanent magnet 14 and the detecting direction 1711 of the 1MTJ element group 13. The magnetic charge density ρ _{s at} the edge of the permanent magnet 14 includes the magnitude of the residual magnetism M _r 141 of the permanent magnet 14, the inclination angle θ _mag of the residual magnetism M _r 141 of the permanent magnet 14, and the inclination angle θ _{sns of the} permanent magnet 14. Is related. The magnetic charge density ρ _{s at} the edge of the permanent magnet 14 can be expressed by the following equation.

The magnetic field H _mag generated by the magnetic charge at the edge of the permanent magnet 14 can be expressed by the following equation.

As shown in FIG. 7, the amount along the direction perpendicular to the detection direction 1171 of the first MTJ element group 13 in the magnetic field H _mag generated by the magnetic charge at the edge of the permanent magnet 14 is defined as a bias magnetic field H _cross . When θ _mag = θ _sns = π / 2, the bias magnetic field H _cross can be expressed by the following equation.

From the equation (4), the bias magnetic field H _cross at the location of the first MTJ element group 13 is adjusted by adjusting the shape and size of the two permanent magnets 14, the gap G between the two permanent magnets 14, and the size of the residual magnetism M _r 141. Can be changed. By changing the bias magnetic field H _cross , the saturation magnetic field of the first MTJ element group 13 can be adjusted, and the sensitivity of the first MTJ element group 13 can be determined.

The bias magnetic field H _cross can also be expressed by the following equation.

The amount H _off along the detection direction 1171 of the first MTJ element group 13 in the magnetic field H _mag generated by the magnetic charge at the edge of the permanent magnet 14 can also be expressed by the following equation.

From the equation (6), the first MTJ element group 13 in the magnetic field H _mag generated by the magnetic charge at the edge of the permanent magnet 14 is adjusted by adjusting the shape and size of the permanent magnet 14 and the inclination angle θ _mag of the residual magnetism M _r 141. The amount H _off along the detection direction 1171 of the first MTJ element 11 can be changed, so that the nail coupling magnetic field Ho of the first MTJ element 11 itself can be canceled, and the operating point of the first MTJ element 11 is located in the linear operating range. Can guarantee.

FIG. 8 is a plan view of the physical position of the half bridge 15 in the XY plane. FIG. 9 is an equivalent circuit diagram of the half bridge 15. The half bridge 15 includes two arms 151 and 152. For example, one first MTJ element group 13 is adopted for the two arms, and the resistance values of the two arms are R1 and R2, for example. Both the detection directions of the arm 151 and the arm 152 are along the detection direction 1171. As shown in FIG. 8, the external magnetic field H _apply whose magnetic field intensity has changed with the gradient is applied along the detection direction 1171, and the magnetic field strength of the external magnetic field H _apply at the physical position where the arm 151 is located is It differs from the magnetic field strength of the external magnetic field _Happly at the physical location where it is located. A pair of inclined permanent magnets 14 are arranged on both sides of the arm 151 and the arm 152. The two input terminals of the half bridge 15 are IN1 and IN2, for example, the input terminal IN2 is connected to the ground. The output terminal of the half bridge 15 is OUT1. A stable voltage V _bias is applied between the input terminal IN1 and the input terminal IN2, and the magnitude of the change in the resistance value R1 of the arm 151 is different from the magnitude of the change in the resistance value R2 of the arm 152. The signal V _OUT1 = V 1 is output.

FIG. 10 is a plan view of the physical position of the full bridge 16. FIG. 11 is an equivalent circuit diagram of the full bridge 16 shown in FIG. The full bridge 16 includes four arms 161, 162, 163, 164, and the four arms all employ two first MTJ element groups 13 connected in series, and the resistance of the four arms is R3, R4, R5 and R6, respectively. The detection directions of the arm 161, the arm 162, the arm 163, and the arm 164 are all along the detection direction 1171. An external magnetic field H _{apply in} which the magnetic field intensity changes with the gradient is applied along the detection direction 1171. As shown in FIG. 10, the magnetic field strength of the external magnetic field H _apply at the physical position where the arm 161 and the arm 162 are located is different from the magnetic field strength of the external magnetic field H _apply at the physical position where the arm 163 and the arm 164 are located. ing. A pair of inclined permanent magnets 14 are disposed on both sides of each arm 161, arm 162, arm 163, and arm 164. Two input terminals of the full bridge 16 are IN3 and IN4. For example, the input terminal IN4 is connected to the ground. The two output terminals of the full bridge 16 are OUT2 and OUT3. A stable voltage V _bias is applied between the input terminal IN3 and the input terminal IN4, the magnitude of the change in the resistance value R3 of the arm 161 or the resistance value R4 of the arm 162, and the resistance value R5 of the arm 163 or the resistance value R6 of the arm 164. Therefore, the output terminal OUT2 and the output terminal OUT3 output voltages V2 and V3, respectively, and the output voltage signal of the full bridge 16 is V _OUT2 = (V3−V2).

In the ideal state, the voltage signal _VOUT2 output from the full bridge 16 does not respond to the common mode magnetic field _HcM, but responds to the differential mode magnetic field _HdM . Due to the action of the common mode magnetic field _HcM , the change in the resistance value of the arm 161, the arm 162, the arm 163, and the arm 164 is the same, so the full bridge 16 does not output a voltage signal. In an ideal state, the resistance value of the four arms of the full bridge 16 are both in R, i.e., R3 = R4 = R5 = R6 = R, and the sensitivity of the four arms of the full bridge 16 are both in _{S R,} That is, S _R3 = S _R4 = S _R5 = S _R6 = S _R , and therefore, the following equation is obtained.

From Equation (9), it can be seen that the voltage signal output from the full bridge 16 is related only to the differential mode magnetic field H _dM and not related to the common mode magnetic field H _cM . Therefore, the full bridge 16 has a great ability to suppress interference of the common mode magnetic field _HcM . A typical output of the full bridge 16 is as shown in FIG.

In actual applications, the sensor may employ two full bridges, i.e. a double full bridge. FIG. 13 is a plan view of the physical position of the double full bridge 17. FIG. 14 is an equivalent circuit diagram of the double full bridge 17. The double full bridge 17 includes eight arms 171, 172, 173, 174, 175, 176, 177 and 178, all of which employ, for example, three first MTJ element groups 13 connected in parallel. The resistance values of the eight arms are R7, R8, R9, R10, R11, R12, R13, and R14, respectively. As shown in FIG. 14, for example, the arm 171, the arm 172, the arm 173, and the arm 174 constitute one full bridge, and the arm 175, the arm 176, the arm 177, and the arm 178 constitute one full bridge. Yes. Preferably, the detection directions of the eight arms related to the double full bridge 17 are both along the detection direction 1171. An external magnetic field H _{apply in} which the magnetic field intensity changes with the gradient is applied along the detection direction 1171. As shown in FIG. 13, the magnetic field strength of the external magnetic field H _apply at the physical position where the arm 171 and the arm 172 are located is different from the magnetic field strength of the external magnetic field H _apply at the physical position where the arm 173 and the arm 174 are located. The magnetic field strength of the external magnetic field H _apply at the physical position where the arm 175 and the arm 176 are located is different from the magnetic field strength of the external magnetic field H _apply at the physical position where the arm 177 and the arm 178 are located. A pair of inclined permanent magnets 14 are arranged on both sides of each arm of the double full bridge 17. Two input ends of the double full bridge 17 are IN5 and IN6. For example, the input end IN6 is connected to the ground. Four output terminals of the double full bridge 17 are OUT4, OUT5, OUT6, and OUT7. A stable voltage V _bias is applied between the input terminal IN5 and the input terminal IN6, the magnitude of the change in the resistance value R7 of the arm 171 or the resistance value R8 of the arm 172, and the resistance value R9 of the arm 173 or the resistance value R10 of the arm 174. The magnitude of the change in the resistance value R11 of the arm 175 or the resistance value R12 of the arm 176 is different from the magnitude of the change in the resistance value R13 of the arm 177 or the resistance value R14 of the arm 178. The terminal OUT4, the output terminal OUT5, the output terminal OUT6, and the output terminal OUT7 output voltages V4, V5, V6, and V7, respectively. The double full bridge 17 outputs two voltage signals V _OUT4 = (V5−V4) and V _OUT5 = (V7−V6).

  In the actual manufacture of the magnetoresistive sensor, the half bridge 15, the full bridge 16 and the double full bridge 17 are all manufactured once on the same substrate using the same process and are usually referred to as a single chip magnetoresistive sensor. Alternatively, a plurality of first MTJ elements 11 are manufactured by the same process on the same substrate, and then the plurality of first MTJ elements 11 are cut and packaged independently, and the first MTJ elements 11 are electrically connected by lead wires. As a plurality of first MTJ element groups 13, the plurality of first MTJ element groups 13 are further electrically connected to the half bridge 15, the full bridge 16, or the double full bridge 17. A single chip packaged magnetoresistive sensor or a multichip packaged magnetoresistive sensor is connected to an application specific integrated circuit (ASIC) or a lead wire of a lead frame via its pads.

As shown in FIG. 15, the magnetoresistive gear sensor 18 provided in this embodiment includes a magnetic sensor chip 181, a permanent magnet 182, a control circuit 183, a concave soft magnetic body 184, and a casing 185. The magnetic sensor chip 181, the permanent magnet 182, the control circuit 183, and the soft magnetic body 184 are concentrated in the casing 185. The magnetic sensor chip 181 includes at least one bridge, and the bridge is a half bridge 15, a full bridge 16 or a double full bridge 17, and each arm of the half bridge 15, the full bridge 16 or the double full bridge 17 has at least one first bridge. The first MTJ element group 13 includes a plurality of first MTJ elements 11 connected in series and / or in parallel. The magnetic sensor chip 181 is electrically connected to the control circuit 183. The soft magnetic body 184 is disposed between the magnetic sensor chip 181 and the permanent magnet 182, and the opening of the soft magnetic body 184 faces the magnetic sensor chip 181. In this embodiment, the magnetic sensor chip 181 includes one double full bridge 17, and each arm of the double full bridge 17 includes one first MTJ element group 13. The permanent magnet 182 generates an external magnetic field H _apply and magnetizes a gear made of a ferromagnetic material. The soft magnetic body 184 ensures that the first MTJ element 11 in the magnetic sensor chip 181 is operated within the linear operation range by reducing the amount along the detection direction 1171 in the external magnetic field H _apply generated by the permanent magnet 182. To do. When relative motion occurs between the gear and the magnetic sensor chip 181, the magnetic field strength of the external magnetic field H _apply at the location of the magnetic sensor chip 181 changes. The magnetic sensor chip 181 detects a change in the magnetic field strength of the external magnetic field H _apply at the physical position where the magnetic sensor chip 181 is located, and outputs a voltage signal to the control circuit 183. The control circuit 183 performs processing and conversion on the voltage signal output from the magnetic sensor chip 181. In this embodiment, the control circuit 183 can convert the sine wave voltage signal output from the magnetic sensor chip 181 into a rectangular wave voltage signal.

In the present embodiment, as shown in FIG. 15, for example, the magnetoresistive gear sensor 18 is stationary and the gear moves. For example, a sinusoidal voltage signal output from the magnetoresistive gear sensor 18 when different position points A, B, C, D, and E of the gear sequentially pass through the magnetoresistive gear sensor is as shown in FIG. The specific position of the tooth to be measured can be determined based on, for example, the correspondence between the sine wave that is the voltage signal output from the magnetoresistive gear sensor 18 and the position point. When the gear teeth are missing, the sine wave and rectangular wave voltage signals output from the magnetoresistive gear sensor 18 are as shown in FIG. Based on, for example, a sine wave or a rectangular wave that is a voltage signal output from the magnetoresistive gear sensor 18, it can be determined whether or not the gear teeth are missing. When the tooth of the gear is missing, the specific position of the missing tooth can be determined based on the correspondence between the voltage signal output from the magnetoresistive gear sensor 18, for example, a sine wave or rectangular wave, and the position point. To adopt double full-bridge 17 to the magnetic sensor chip 181 of the magnetoresistive gear sensor 18 which is provided in this embodiment, the magnetoresistive gear sensor 18 can output a voltage signal V _OUT4 and V _OUT5 two systems, FIG. As shown in FIG. 18, the movement direction of the gear can be determined based on the phase difference between the two voltage signals V _OUT4 and V _OUT5 . When the magnetoresistive gear sensor 18 is applied, an interference magnetic field other than the external magnetic field H _apply generated by the permanent magnet 182 can be used as a common mode magnetic field at the position where the magnetic sensor chip 181 is located. Since the double full bridge 17 is employed in the magnetic sensor chip 181 and the double full bridge has a high capability of suppressing interference due to the common mode magnetic field, the magnetoresistive gear sensor 18 is not an external magnetic field H _apply generated by the permanent magnet 182. It becomes difficult to receive interference by the interference magnetic field.

<Example 2>
FIG. 19 is a schematic diagram of the structure of the second MTJ element 21 provided in the present embodiment. As shown in FIG. 19 , the second MTJ element 21 has a multilayer structure. The insulating layer 212, the bottom electrode layer 213, the pinning layer 214, the pinned layer 215, and the tunnel barrier layer 216 are sequentially deposited on the substrate 211. , A magnetic free layer 217, a bias layer 218, and a top electrode layer 219. The pinned layer 215 and the magnetic free layer 217 are ferromagnetic layers. The material of the pinned layer 215 and the magnetic free layer 217 includes, for example, Fe, Co, Ni, FeCo, FeNi, FeCo, or FeCoNi. The pinned layer 215 may be a composite layer formed of a ferromagnetic layer, a Ru layer, and a ferromagnetic layer. For example, the pinned layer 215 is a composite layer formed of a FeCo layer, a Ru layer, and a FeCo layer. The pinning layer 214 is an antiferromagnetic layer, and the material thereof includes, for example, PtMn, IrMn, or FeMn. Due to the exchange coupling between the pinning layer 214 and the pinned layer 215, the direction 2151 of the magnetic moment of the pinned layer 215 is fixed in one direction, and the direction 2151 of the magnetic moment does not change by the action of the external magnetic field _Happly . The material of the tunnel barrier layer 216 includes, for example, MgO or Al ₂ O ₃ . The direction 2171 of the magnetic moment of the magnetic free layer 217 can be changed with the change of the external magnetic field _Happly . Due to the action of the external magnetic field H _apply , the magnetic moment direction 2171 of the magnetic free layer 217 gradually changes from a direction parallel to the magnetic moment direction 2151 of the pinned layer 215 to a direction antiparallel to the magnetic moment direction 2151 of the pinned layer 215. It is possible to change and vice versa. The bias layer 218 is an antiferromagnetic layer or a permanent magnetic layer. Due to the exchange coupling between the bias layer 218 and the magnetic free layer 217, the bias layer 218 can be provided with a bias magnetic field H _cross orthogonal to the detection direction of the second MTJ element 21 for the magnetic free layer 217. By changing the bias magnetic field H _cross , the saturation magnetic field of the second MTJ element 21 can be adjusted, and the sensitivity of the second MTJ element 21 can be further adjusted. When the bias layer 218 is an antiferromagnetic layer, the blocking temperature of the bias layer 218 is lower than the blocking temperature of the pinning layer 214. In order to reduce the bias magnetic field H _cross provided by the bias layer 218, an isolation layer may be deposited between the magnetic free layer 217 and the bias layer 218. By changing the thickness of the isolation layer, the magnitude of the bias magnetic field H _cross can be adjusted. Normally, a nonmagnetic material such as Ta, Ru or Cu is employed for the isolation layer. Usually, a nonmagnetic conductive material is used for the top electrode layer 219 and the bottom electrode layer 213. As the material of the substrate 211, silicon, quartz, heat-resistant glass, GaAs or AlTiC is usually used. The area of the insulating layer 212 is larger than the area of the bottom electrode layer 213. The top electrode layer 219 and the bottom electrode layer 213 are used for electrical connection with other elements.

  In application, a plurality of second MTJ elements 21 can be connected in series and / or in parallel to form one second MTJ element group 23. In the present embodiment, the second MTJ element group 23 is formed, for example, by connecting four second MTJ elements 23 in parallel, and the detection directions of the four second MTJ elements 21 related to the second MTJ element group 23 are the same. is there. The second MTJ element group 23 is electrically connected to other elements, for example, the ohmmeter 12. One second MTJ element group 23 can be used as one arm of the bridge, and a plurality of second MTJ element groups 23 connected in series and / or in parallel can be used as one arm of the bridge. What should be explained is that when the second MTJ element group 23 is employed in the bridge, it is not necessary to provide the inclined permanent magnets 14 on both sides of the second MTJ element group 23. In the present embodiment, for example, one second MTJ element group 23 is employed for each arm of the half bridge 15, the full bridge 16, and the double full bridge 17.

  The situation in which the second MTJ element group 23 is adopted for the magnetoresistive gear sensor 18 is the same as in the first embodiment.

  The sensor uses an MTJ element as a sensing element, and the sensor has better temperature stability, higher sensitivity, lower power consumption, better linearity than a sensor using a Hall element, AMR element, or GMR element as a sensing element. Wide linear operating range and simple structure. The sensor is provided with a concave soft magnetic material, and by reducing the amount along the detection direction of the MTJ element in the external magnetic field generated by the permanent magnet, the MTJ element in the magnetic sensor chip is within its linear operating range. It can be guaranteed to operate, and the performance of the sensor can be greatly improved. By adopting a full bridge for the magnetic sensor chip of the sensor, the sensor is less susceptible to interference by an interference magnetic field other than an external magnetic field generated by a permanent magnet. In one preferred embodiment, a pair of inclined permanent magnets are arranged on both sides of the MTJ element, and the amount perpendicular to the detection direction of the MTJ element in the magnetic field generated by the inclined permanent magnet is a bias magnetic field applied to the MTJ element. The saturation magnetic field of the MTJ element can be adjusted by changing the bias magnetic field, whereby a highly sensitive sensor can be obtained, or a sensor with a different sensitivity can be realized as required. it can. In one preferred embodiment, a pair of inclined permanent magnets are arranged on both sides of the MTJ element, and the amount along the detection direction of the MTJ element in the magnetic field generated by the inclined permanent magnet is equal to the nail coupling magnetic field of the MTJ element. Can be canceled, thereby ensuring that the operating point of the MTJ element is in its linear operating range and improving the linearity of the sensor. In another preferred embodiment, a bias layer is disposed on the magnetic free layer of the MTJ element, and the bias layer can provide a bias magnetic field perpendicular to the sensing direction of the MTJ element to the magnetic free layer. By changing the magnetic field, the saturation magnetic field of the MTJ element can be adjusted, whereby a highly sensitive sensor can be obtained, or a sensor with a different sensitivity can be realized as required. The sensor can determine the position of the gear teeth, and can determine the position of the missing teeth even if the gear teeth are missing. The sensor can determine not only the speed of movement of the gear but also the direction of movement of the gear. The sensor applies not only to linear gears but also to circular gears. Sensors are advantageous for realizing large-scale production at low cost.

  It should be understood that the detailed description given to the technical idea of the present invention using the above preferred embodiments is merely an example and does not limit the present invention. A person skilled in the art can modify the technical idea described in each embodiment based on the specification of the present invention, or equivalently replace a partial technical feature therein. The essence of the corresponding technical idea does not depart from the spirit and scope of the technical idea of each embodiment of the present invention.

Claims (7)

Including a magnetic sensor chip (181) and a first permanent magnet (182),
The magnetic sensor chip (181) includes at least one sensor bridge including a plurality of bridge arms;
Each arm of the bridge includes at least one MTJ element group (13, 23), the at least one MTJ element group is a plurality of MTJ element groups, and the plurality of MTJ element groups are connected in series and / or in parallel. Has been
The MTJ element groups have the same detection direction, and the detection direction is parallel to the free layer;
Each MTJ element (11) has a multilayer structure, and includes a pinning layer (114), a pinned layer (115), a tunnel barrier layer (116), and a magnetic free layer (117), which are sequentially deposited,
The magnetoresistive gear sensor further includes a concave soft magnetic body (184) disposed between the magnetic sensor chip (181) and the first permanent magnet (182), and the soft magnetic body The opening of (184) faces the magnetic sensor chip (181),
The sensor chip has a full-bridge (16), the half-bridge (15) or double full bridge (17),
The magnetoresistive gear gear sensor is further disposed between the first permanent magnet and the sensor chip ,
The magnetoresistive gear gear sensor further has an external housing structure ,
A pair of second permanent magnets (14) is provided on both sides of each MTJ element group (13). In order to cancel the nail coupling magnetic field of the MTJ element group (13), each pair of second permanent magnets (14 ) Are arranged inclined with respect to the detection direction of the corresponding MTJ element group (13),
The amount H _off along the detection direction (1171) of the first MTJ element group (13) in the magnetic field H _mag generated by the magnetic charge at the edge of the second permanent magnet (14) is represented by the following magnetoresistive gear: Sensor.

Here, the magnetic field H _mag is the magnetic field at the gap position between the two permanent magnets (14), and θ _mag is the inclination angle of the residual magnetism M _r 141 of the permanent magnet 14 . Furthermore, in order to provide a bias magnetic field to the MTJ element group (13), each pair of second permanent magnets (14) is disposed perpendicular to the detection direction of the corresponding MTJ element group (13). The magnetoresistive gear sensor according to claim 1. In order to further cancel the nail coupling magnetic field of the MTJ element group (13), each pair of second permanent magnets (14) is arranged to be inclined with respect to the detection direction of the corresponding MTJ element group (13). The magnetoresistive gear sensor according to claim 2 . Each MTJ element (21) has a multilayer structure, and is sequentially deposited pinning layer (214), pinned layer (215), tunnel barrier layer (216), magnetic free layer (217), and bias layer (218). The magnetoresistive gear sensor according to claim 1 , comprising: The magnetoresistive gear sensor according to claim 4 , wherein each MTJ element (21) further includes an isolation layer provided between the magnetic free layer (217) and the bias layer (218). The magnetoresistive gear sensor further includes a control circuit (183) electrically connected to the magnetic sensor bridge;
The control circuit (183) determines a tooth position based on a correspondence relationship between a voltage signal output from the magnetic sensor chip (181) and a tooth position of a gear. The magnetoresistive gear sensor as described. The magnetic sensor chip (181) includes a double full bridge, each arm of the double full bridge includes an MTJ element group, and the control circuit determines a movement direction of a gear based on a voltage signal output from the magnetic sensor chip. The magnetoresistive gear sensor according to claim 6 , wherein the magnetoresistive gear sensor is fixed.

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